Positively charged coated silica particles as first disclosed in U.S. Pat. No. 3,007,878 by Alexander and Bolt have a variety of properties which make them unique and distinctly different from the previously known negatively charged silica and modified silica sols. However, the commercial exploitation of sols of positively charged silica particles has been limited by stability problems.
Some methods have been proposed by which the stability of sols of positively charged silica particles can be improved. While each method has its advantages, most require several or more steps in order to carry out the stabilization process. For example, in U.S. Pat. No. 3,252,917, Mindick and Thompson disclose a stabilization method which requires a minimum of five steps not including regeneration of the two types of ion exchange resins employed. Such a process is costly and cumbersome as well as time consuming. On the other hand, the process for preparing improved positive sols disclosed in U.S. Pat. No. 3,719,607 to Earl P. Moore is somewhat less costly and time consuming but nevertheless requires at least three different operations, including an aging step which must be conducted until the pH remains constant. While the Moore process yields a distinct improvement in the stability of silica sols, nevertheless it is sufficiently cumbersome and time consuming to render it less than optimally attractive on a commercial basis.